Mitochondrial creatine kinase binding to liposomes and vesicle aggregation: effect of cleavage by proteinase K

Mitochondrial creatine kinase and its proteinase K nicked-derivative interaction with liposomes induced slight secondary structure changes evidenced by infrared spectra. In nondenaturing conditions, the N-terminal (K₁) and the C-terminal (K₂) fragments remained associated with each other and bound to liposomes. When the two fragments were separated by denaturation, K₂ was soluble, whereas most of K₁ was adsorbed onto liposomes. The three-dimensional structure of uncleaved mtCK suggests that the C-terminal moiety, which contains positively charged surface residues, interacted with membranes. After denaturation and renaturation of the nicked enzyme, both peptides did not refold properly and did not reassociate with each other. The misfolded K₁ fragment bound to the membrane through a stretch of positive residues, which were buried in the native enzyme. The lack of binding of the ill-folded K₂ peptide could be related to the disruption of the optimal disposition of its positive charges, responsible for the correct interaction of native mtCK with membrane.